VQFN Packages
Q. What recommendations can CML provide to me when considering the use of the VQFN (Very Thin Quad Flat Non-leaded) package and what is the best way to attach a CML device supplied in this package to my PCB?

A. CML supplies a number of devices in VQFN packaging. Due to their compact size, the devices available in these package types are called "Qx" packages, where x is a reference to the number of pins available (eg Q1 = 64 pins).
CML advises that special care should be taken when assembling any Qx (e.g. Q1 64 pin VQFN) packages on to a PCB.
In some cases, such as the CMX990 and the CMX998, it is necessary for both electrical and thermal dissipation reasons to attach the central exposed pad to a ground plane on the PCB.
In other cases, unless stated to the contrary, it is not essential for electrical or thermal dissipation reasons to make such connection, however CML would still recommend that this pad be soldered down to the PCB so as to provide good physical attachment. If this is done, the PCB land to which it is attached should be electrically unconnected to other parts of the PCB.

The following link will take the reader to a CML guidance note on using the CML VQFN package. It provides comprehensive guidance for assembling such packages into an application. [VQFN PCB Design Guidance Notes]

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